Wireless communication has seen tremendous growth in recent years and is becoming widely applied to personal and business computing. Wireless access is broadening network reach by providing convenient and inexpensive access in hard-to-wire locations. Of major benefit is the increased mobility wireless local area networks (WLANs) allow. Wireless LAN users can roam seemingly without restriction and with access from nearly anywhere without being bounded by conventional wired network connections.
One of the most significant issues in the area of wireless and mobile communications technology is the provision of constant IP (Internet protocol)-connectivity to mobile nodes upon roaming. While the IEEE 802.11 standard for WLANs acts as an important milestone in the evolution of wireless networking technology, roaming has not yet gained much coverage in the current IEEE 802.11 standard, resulting in insufficient support of key mobility functions.
Referring concurrently to FIGS. 1 and 2, a typical IEEE 802.11 infrastructure WLAN environment consists of access points 10a, 10b, 10c, 10d, 10e (APs) and mobile terminals/stations 12a, 12b (STAs) communicating over the air via 802.11b specific messages. Neighboring APs are attached to a wired distribution system 14 (DS) and form an extended service set 16a, 16b, 16c, 16d (ESS). Upon power up, a STA 12a gets associated to an AP 10a inside the ESS 16a within which it is residing via specific association messages. At the same time, it obtains an IP address (e.g., via DHCP, Dynamic Host Configuration Protocol) so as to be widely reachable at its current location. Furthermore, certain authentication procedures take place (e.g., 802.1x authentication) in order to authenticate the STA 12a. The IP subnet 18a where the STA's IP address belongs is called the home network (HN). Every time the STA 12a powers up inside an ESS 16a, the IAPP (Inter-Access Point Protocol) is triggered so as to inform the neighboring APs 10b about the STA's 12a physical location. This is accomplished via specific layer 2 (L2) message updates sent by the home access point (HAP) 10a to the subnet broadcast address. Routing of the IP datagrams is performed via standard IP routing mechanisms. The APs 10a, 10b are used as L2 bridges. Any packets sourcing outside the HN and destined to the STA 12a, arrive at the gateway router 20a of the corresponding ESS 16a. Inside the ESS 16a, specific L2 bridging takes place to successfully deliver packets to the STA's actual location.
Within the ESS 16a, the STAs 12a, 12b may roam from one AP (e.g., 10a) to another AP (e.g., 10b) via reassociation messages. In an 802.11 WLAN, each time a STA 12a is reassociating to a new AP 10b inside the ESS 16a of its HN, it performs an intra-network handover. The L2 point of attachment has changed to the MAC address of the new AP 10b, and the new AP 10b becomes the STA's HAP (home AP). The STA 12a preserves its MAC address. The time elapsed between the cut-off of the previous AP-STA and the connection running between the new AP and the STA is called the handover period or handover recovery time. During this period, any active sessions that this STA 12a had before its movement get disconnected. The L2 handover of 802.11 STAs is supported by the IAPP protocol, which provides the necessary means for quick recovery of the interrupted active sessions. Moreover, it assures that the STA is still able to send/receive IP packets from its new location while preserving its home IP address.
For inter-network handover in IEEE 802.11 WLANs, the STA 10a moves inside an ESS 16b that belongs to a different IP subnet, i.e., it triggers a layer 3 (L3) handover. This type of handover is performed when a roaming STA 12a reassociates to a foreign AP 10c of an ESS 16b outside of its home network and involves both an L2 and an L3 handoff. (Similarly, if a STA already lying in a foreign network roams inside/between foreign networks, it still performs an L3 handover.) Thus, via specific 802.11 MAC layer mechanisms, the STA 12a is now physically attached to a foreign AP 10c. However, it was not one of the IAPP objectives to provide support for inter-network (L3 or IP) handover of 802.11 roaming STAs. Accordingly, any packets now destined to the home address of the STA 12a are routed to its HN. However, these packets will be dropped due to the fact that the STA 12a does not physically belong there anymore. Similarly, any packets originated from the STA 12a will be dropped inside the foreign network, because their source IP address does not belong to this subnet.
All of these routing issues arising upon an L3 handover form a problem that is outside the scope of the IAPP. With the increasing deployment of 802.11 networks in both commercial and home environments, the need for inter-network handover increases. The present invention addresses this need, ensuring constant IP-connectivity during any type of handover (IP or MAC layer) to assist in unbounded roaming of 802.11 STAs.